1. Field of the Invention
The present invention relates to cabs of heavy construction vehicles, and more particularly to cabs of heavy construction vehicles with an openable front window and a locking device therefor.
2. Description of Prior Art
Generally, cabs of heavy construction vehicles such as cranes or excavators have the box shape, side walls of which have openings each provided with a glass window. An example of such type of cabs is shown in FIGS. 4 and 5 and designated by reference numeral 50. In particular, a front wall 51 of the cab 50 has the frontwards protruded shape from a perpendicular plane so that interior of the cab can widen to provide a space for various driving devices and control devices therein. The front wall 51 comprises a flat front wall upper portion 51a inclined rearwards as extending downwardly and a flat front wall lower portion 51b inclined rearwards as extending downwardly from the lower end of said upper portion 51a. The upper portion 51a has an opening provided with a front glass window 52 which is capable of being lifted up to allow the opening to be opened. To this end, The cab 50 includes a pair of guide rails 54 attached to both side of said cab 50 and extending from the lower end of the opening of the front wall upper portion 51a and the upper end of the opening of the front wall upper portion 51a along the side edges of the opening, respectively. To each side edges of the front window 52, a frame 55 is attached which extends throughout the length of said front window 52 and has rollers 56 at its upper and lower ends, respectively. The rollers 56 of the frame 55 are positioned in the guide rails 54 in order to guide the opening/closing movements of the front window 52 by rolling and sliding along the guide rails 54 during opening/closing operations of the front window 52.
However, when the front window 52 of the cab 50 is forced to move upwardly or downwardly in opening/closing operations, upper and lower rollers 56 respectively roll and slide along their straight traces on individual guide rails 54, guide directions of which are different from each other as shown in FIG. 1. Thus, the opening/closing operations may not be carried out smoothly. Also, during the movement, the front window 52 occupies a considerable part of a front space inside the cab 50 as shown in FIG. 5 so that a sufficient space can not be secured between the person operating the vehicle and the moving window. Therefore, there may be a danger that the person is carelessly struck on his body to be injured by the moving window.
Also, the cab 50 is provided with a locking device 60 for locking the window 52 at its desired positions. However, the locking of the front window 52 provided by the locking device 60 are limited only to a full opening position and a full closing position. That is, there is a disadvantage that the front window 52 can not be locked at an optionally desired position between its full opening and closing positions. This is because if the front window 50 is locked at an intermediate position between its full opening and closing positions, it would occupy much front space inside the cab 50.
As shown in FIG. 6, the window locking device 60 of the cab 50 includes a hollow locking member 61 mounted at the upper portion of the window frame 55 and provided with a reversed U-shaped slot 61a. Positioned inside the locking member 61 is a lock bolt shown at 62 which is slidable in said locking member 61. The lock bolt 62 has a handle 62a capable of slidably moving along the reversed U-shaped slot 61a. Also, there is provided a pair of locking apertures 59 perforated through the side wall 58 of the cab 50 in order to lock the window 52 at its full opening and closing positions by receiving a protruding end 62b of the lock bolt 62. But, there is a problem that it is very difficult to accurately align the protruding end 62b of the lock bolt 62 with a desired locking aperture 59 in order to insert the former into the latter for locking the window 52. Also, if the locking was unstable as a result of wear of the locking apertures 59 and the reversed U-shaped slot 61a, the front window 52 will be severely rattled depending upon a vibration of the vehicle during a work on the ground, thereby causing the rattling noise to be generated. Furthermore, the front window may be suddenly dropped or broken.